The present invention relates to a metacarpal anchoring rod, particularly for a trapezo-metacarpal prosthesis. It also relates to a set of modular elements allowing the constitution of such a trapezo-metacarpal prosthesis.
It is well known to restore a trapezo-metacarpal articulation by means of a prosthesis, which can either include only a metacarpal prosthetic element, implanted in the first metacarpal and coming directly into articulation with the trapezium bone, or to include both an metacarpal prosthetic element and a trapezium prosthetic element, each element being implanted in its corresponding bone and coming into articulation with the other element.
The metacarpal element often consists of two parts assembled one to the other, to with an elongated and tapered part constituting an anchoring rod to the first metacarpal and an articulation part forming an articulating surface.
A trapezo-metacarpal prosthesis can in any case be of the type called “anatomical,” wherein prosthetic articulation surface(s) reproduce more or less the shape of the native articulation surface(s), which have an aspect in the form of a “saddle”; they can also be of the type called “guided,” wherein the articulation of the prosthetic elements is accomplished by means of a ball formed by a spherical head forming a part of the metacarpal element and by a receiving cup accommodating this spherical head, the cup constituting the trapezium element.
The anchoring rods which are formed by the metacarpal elements of the known prostheses have the considerable disadvantage of not presenting a shape that is perfectly adapted to that of the marrow channel of the first metacarpal. Moreover, the more or less conical form of the marrow channel of this first metacarpal can have a certain tendency to eject such an anchoring rod.